body{
  font-size: 20px;
  color: red;
  p{
    font-size: 30px;
    color: blue;
    &:before{
      font-size: 13px;
      content: 'aaaa';
      display: inline-block;
      color: blueviolet;
    }
  }
  .img_box{
    width: 60px;
    height: 50px;
    background:url('./imgs/key.png');
    background-size: 60px 50px;
  }
}